D124 — Rule relaxation spent on signals, not power nets

Decision

A rule relaxation (the rule-escalation ladder of the real-world study) is spent on signals, not on power nets: power and ground nets stay at the board's own clearance and via sizes (class copies) and the router's new option --no-neck-nets stops its neck-down for them (doc 05 §45). A relaxed routing counts as routed only after a safety simulation (reports/realworld/py/safety.py: ngspice crosstalk on the extracted copper of every compromised signal pair, IPC-2221 and DC drop for narrowed nets, via impedance, with stated assumptions) does not FAIL.

Reason

Owner's rule (2026-10-17): power nets have less margin to play with than signals, and pushing a rule needs proof that it is safe.

Consequences

Power nets that only route by necking down now stay unrouted (the board is then reported as open, not hidden); the verdict rests on assumed drivers, loads and currents.